Sigma 70-300mm f/4-5.6 DG Macro (Nikon AF)

I'm thinking about getting a new lens for my dads Nikon D70. When I have the money for my own camera I'll probably invest in the D50 or something else if they've come with something new by then. Therefore it makes sense to invest in a lens for my dads digital rather than my budget canon film slr. My dad lets me use his D70 most of the time anyway.